cis-Diamminedichloroplatinum (II) (cisplatin, CDDP) is a widely used chemotherapeutic agent. While many tumors are highly responsive to CDDP, certain tumors are resistant to this drug which limits its efficacy. The anti-tumor activity of CDDP is believed to result from its covalent interaction with chromosomal DNA. Alterations in tumor cell sensitivity to CDDP may result from the presence or absence of protein(s) which specifically recognize CDDP-damaged DNA. We have developed a novel DNA affinity precipitation assay that allows the direct identification of cellular proteins that bind to CDDP-damaged DNA. Two of these proteins have been identified as high mobility group proteins (HMG) l and 2. These proteins have been selected for further study because: l) they specifically recognize and bind with high affinity to the intrastrand adducts formed by CDDP, 2) increased expression of HMG2 is observed in HeLa lines which are less sensitive to CDDP toxicity, 3) these proteins are primarily present in the nucleus and are major chromosomal proteins, 4) under conditions where HMG1 and HMG2 bind to CDDP-DNA, other chromosomal proteins with similar characteristics do not, and 5) they exhibit widespread distribution in cells of different histological types. The goals of this project are to fully characterize the binding of HMG1 and HMG2 to CDDP-DNA, determine whether these proteins participate in the excision/repair of CDDP-DNA adducts, conduct functional studies to determine whether increased or decreased levels of HMG2 effect the sensitivity of cells to CDDP and determine the relationship between the levels of these proteins in established human ovarian cell lines and their relative sensitivity to CDDP. We believe that results from these studies will provide important insights into the mechanisms of tumor cell sensitivity to CDDP and could lead to the development of a clinically useful predictive assay for human tumor cell response to the cytotoxic properties of CDDP. The ability to predict which tumors are sensitive to the cytotoxic effects of CDDP would identify individual patients who will benefit from CDDP therapy while patients with nonresponsive tumors would be directed towards potentially more beneficial forms of treatment.